In typical variable blade pitch propulsor systems for aircraft engines, whether of the propeller, propfan or unducted or ducted fan type, a plurality of propulsor blades, each pivotally mounted for movement about its longitudinal axis to a rotary hub driven by the aircraft engine, are operatively connected to a blade pitch change actuator system disposed in an interior chamber defined within the hub. One type of pitch change system, commonly referred to as a rotary actuation system, is disclosed, for example, in commonly-assigned U.S. Pat. Nos. 3,876,334; 3,893,789; 3,895,884; 3,902,822, 3,904,315, 3,964,839 and 4,021,142. Another type of pitch change system, commonly referred to as a linear actuation system, is disclosed, for example, in commonly-assigned U.S. Pat. Nos. 4,753,572 and 4,936,746. In such linear systems, rotation of ballscrew actuator causes a nut threaded thereabout to translate either forwardly or rearwardly along the ballscrew depending upon the direction of rotation of the ballscrew. The ballscrew nut is integral to a surrounding yoke which is operatively connected to each of the blades through a plurality of articulating links, each of which connects to a rotatable trunnion in which a blade is mounted, such that translation of the yoke is converted to a rotation of each blade about its longitudinal axis. In both of these types of pitch change systems, the pitch change actuator has been driven by selectively activating a hydraulic or electric drive mechanism which serves to rotate the pitch change actuator relative to the rotating hub so as to effect a rotation of each the blades within its hub socket about its longitudinal axis, thereby changing the pitch setting of the blade.
As is well recognized by those skilled in the art, it is desirable in such blade pitch change actuation systems to provide a low pitch stop to limit movement in flight to a fine blade pitch below a preselected minimum, for example as might otherwise occur in the event of a malfunction in the system, and also a feather stop to prevent the blades from inadvertently passing through feather. Also, it is necessary that the pitch change system be capable of reversing blade pitch. In conventional systems, blade pitch reversal has customarily been accomplished by passing the blades through flat blade pitch. Accordingly, such conventional systems are unsuitable for use on a propulsor wherein blade pitch reversal is to be accomplished by passing the blades through feather, rather than flat pitch, such as now desired on variable pitch propulsors having a large number of blades, such as advanced ducted propulsors being considered for use on turbine driven aircraft.